1. Field of the Invention
The present invention relates to a method for setting a terminal (user equipment) identifier in a mobile communication system as terminal (user equipment) identification information, when data delivered through a dedicated logical channel is transmitted through a common transport channel. More specifically, it relates to a method for setting a user equipment identifier in a UMTS (Universal Mobile Telecommunications System, European type IMT-2000 radio communication system). As data (RLC SDU; Radio Link Control Service Data Unit) and message type indicator, which serve the purpose of user equipment identification information, are transmitted from a RRC (Radio Resources Control) layer to an RLC (Radio Link Control) layer, the RLC layer sets a user equipment identifier indicator according to the transmitted message type indicator and transmits it with the data to a MAC (Medium Access Control) layer. In turn, the MAC layer adds the appropriate user equipment identification information to the data received.
2. Description of the Related Art
For the purpose of making specifications for third generation mobile communication systems (IMT-2000 systems) based on evolved GSM core network and W-CDMA radio access network and specifications for user equipment for the system, a group of standard developing organizations (SDOs) including ETSI of Europe, ARIB/TTC of Japan, Ti of U.S. and TTA of Korea established a unified SDO in the name of Third Generation Partnership Project (“3GPP”). 3GPP is developing third generation mobile communication systems (IMT-2000 system) providing high performance multimedia services including audio, video and data over a radio network.
For the purpose of efficient management and technological development, five Technical Specification Groups (“TSGs”) are organized under 3GPP. Each TSG is in charge of approving, developing and managing specifications related to a pertinent field. Among them, RAN (Radio Access Network) group has developed functions, requirements and interface specifications related to user equipment and UMTS (Universal Mobile Telecommunications System, European type IMT-2000 System) Terrestrial Radio Access Network (“UTRAN”) in order to set a new radio access network specification to the third generation mobile communication system.
A TSG-RAN group consists of one plenary group and four working groups. WG1 (working group 1) has been developing specifications for a physical layer (first layer), and WG2 has been specifying functions of a data link layer (second layer) and a network layer (third layer). In addition, WG3 has been developing specifications for interfaces among base stations, RNCs (Radio Network Controller) and core networks in the UTRAN. Lastly, WG4 has been discussing requirements for radio link performance and radio resource management.
FIG. 1 illustrates a structure of the UTRAN.
As depicted in FIG. 1, the UTRAN 20 includes a Node B and an RNC. Node B is controlled by the RNC, and works as an access point by receiving uplink information from the user equipment 10 and by transmitting downlink information from the UTRAN through the physical layer linking. The RNC performs allocation and management of radio resources.
The RNC can be classified as either control or serving RNC. First, the control RNC directly manages Node B and manages common radio resources. Next, the serving RNC manages dedicated radio resources allocated to each user equipment.
The control RNC and the serving RNC can be the same. However, when a user equipment moves from a serving RNC's region to other RNC's regions, a control RNC and a serving RNC can be different.
Accordingly, when the control RNC and the serving RNC are different, data to be transmitted to a user equipment is transmitted to a control RNC after passing through a serving RNC and transmitted to a user equipment through a Node B connected to the control RNC.
As depicted in FIG. 1, a Radio Network Sub-system (“RNS”) includes one RNC and several Node Bs. In addition, the RNS where a serving RNC is located is referred to as serving RNS.
FIG. 2 illustrates a structure of a general radio interface protocol according to a radio access network specification of the 3GPP.
A radio interface protocol between a user equipment and the UTRAN is horizontally divided into a physical layer (first layer), a data link layer (second layer) and a network layer (third layer). It is also vertically divided into a control plane for control signaling and a user plane for data information transfer.
As to the vertical division, first, the control plane contains a radio resource control (“RRC”) layer, a radio link control (“RLC”) layer, a medium access control (“MAC”) layer and a physical layer as the first layer. Next, the user plane contains a packet data convergence protocol (“PDCP”) layer, a broadcast/multicast control (“BMC”) layer, an RLC layer, a MAC layer and a physical layer.
The physical layer provides information transfer service to an upper layer by using various radio transfer techniques. It is connected to the MAC layer as an upper layer through transport channels. The data between the MAC layer and the physical layer are transmitted through the transport channels. The transport channels are classified as a DTCH (Dedicated Transport Channel) and a CTCH (Common Transport Channel). The DTCH is a transport channel exclusively used by one user equipment, and the CTCH is a transport channel jointly used by several user equipment.
The MAC layer provides a reallocation service of a MAC parameter for allocating and reallocating radio resources. It is connected to the RLC layer through a logical channel, and various logical channels are provided according to the type of information transmitted. In general, a control channel is used when transmitting information on the control plane, and a traffic channel is used when transmitting information on the user plane.
The RLC layer provides the function of setting and releasing radio links. In addition, it performs segmenting and reassembling functions of an RLC Service Data Unit (“SDU”) delivered from an upper layer on the user plane. The size of the RLC SDU is adjusted on the RLC layer to be suitable for a processing capacity. Afterwards, header information is added, and it is transmitted to the MAC layer as an RLC Protocol Data Unit (“PDU”) format.
Since the PDCP layer is an upper layer of the RLC layer, it converts the data of packet network protocols, such as IPv4 or IPv6, into the data of a format suitable for the RLC layer, and vice versa. In addition, it assists the lower layers to transfer data through the radio interface efficiently by reducing unnecessary control information used in a wire network. That function is referred to as header compression, and, for example, the header compression can be used to reduce TCP/IP header information.
The BMC layer exists on the user plane, and it is used for applying a broadcast service or a multicast service to the system having a radio interface.
The RRC provides information broadcast services to all user equipment located within a certain area. In addition, it performs a control plane signal processing for a control signal exchanging between the third layers of transmitting and receiving side and has functions for setting/maintaining/releasing radio resources between user equipment and the UTRAN. In particular, the RRC has functions for setting/maintaining/releasing a Radio Bearer and allocating/reconfiguring/releasing radio resources required for radio access networking. Herein, the Radio Bearer means a service provided by the second layer for data transfer between the user equipment and the UTRAN. That is, setting a radio bearer means specifying the characteristics of a protocol layer and a channel required to provide a certain services, and setting specific parameters and operation method.
Each user equipment also includes all radio interface layers. However, in the UTRAN, protocol layers are dispersed in several constituent elements of a UTRAN (UMTS Terrestrial Radio Access Network).
FIG. 3 illustrates an example of a protocol layer hierarchy corresponding to the constituent elements of a Radio Access Network. In general, the RLC layer is placed in the serving RNC. The functions of the MAC layer can be divided according to the type of a transport channel and can be placed either in the serving RNC or in the control RNC.
As depicted in FIG. 3, when two RNCs are operated concurrently as a serving RNC and a control RNC, the MAC layer is divided into a MAC-d sub layer and a MAC-c/sh sub layer according to the type of transport channel. These are respectively placed in the serving RNC and the control RNC.
In comparison, when one RNC is operated commonly as the serving RNC and the A) control RNC, a MAC-c/sh sub layer and a MAC-d sub layer are placed on the same RNC. This is because the MAC-d sub layer manages a dedicated logical channel, which is dedicated to a user equipment, and the MAC-c/sh sub layer manages a common transport channel. Because the MAC-s/sh sub layer manages the common transport channel, which is jointly used by all user equipment within the cell, each cell has one MAC-c/sh layer. Because the MAC-d sub layer provides a dedicated service to a user equipment, and one MAC-d sub layer exists for each one user equipment. The physical layer (PHY) is placed in the Node B.
FIG. 4 illustrates a structure of an RLC layer and a MAC layer in the UTRAN. In a down_link, when data is delivered to the RLC layer from an upper layer, the RLC layer stores an RLC PDU in an RLC buffer and transmits a certain number of PDUs corresponding to a request from the MAC layer.
The RLC PDU received in the MAC-d layer is transmitted through Dedicated Transport Channel (DTCH) or Common Transport Channel (CTCH) by channel switching. When it is transmitted through DTCH, a related header is added to it in the MAC-d sub layer, and it is transmitted to the physical layer through a Dedicated Channel (DCH).
However, the RLC PDU is transmitted through the CTCH, it is transmitted from the MAC-d sub layer to the MAC-c/sh sub layer, and a related header is added on. Thereafter, it is multiplexed through other logical channels and is transmitted through the common transport channel such as PCH (Paging Channel), FACH (Forward Access Channel) and DSCH (Downlink Shared Channel) etc.
In an up_link, data is received through the Dedicated Channel (DCH) and the common transport channel (CTCH) such as RACH (Reverse Access Channel) and CPCH (Common Packet Channel) etc., and the data is subsequently transmitted to an upper layer.
In that case, the data is transmitted to the RLC layer via the path converse in the down_link. The structures of the RLC layer and the MAC layer in the user equipment are almost the same as the structure in FIG. 4.
To illustrate, the transmission of data through FACH (Forward Access Channel) as the common transport channel will be described with reference to FIG. 4.
Because the RLC PDU transmitted from the RLC layer uses the FACH of the MAC-c/sh sub layer, it is transmitted to the MAC-c/sh sub layer through channel switching and control transmission multiplexing. The control transmission multiplexing means multiplexing several logical channels.
Data transmitted to the MAC-c/sh sub layer is multiplexed with data of other logical channels. In addition, because the data of various user equipment can be transmitted through the common transport channel, to identify a user equipment to receive pertinent data, a destination user equipment's identifier is added to the MAC PDU through a user equipment identifier inserting for data multiplexing. Herein, a TCTF (Target Channel Type Field) mapping for data multiplexing maps the relationship between the logical channel and the transport channel. Data mapped by the FACH transport channel is transmitted to the FACH based on a data transmission schedule by considering the priority of the user equipment.
The RLC PDU delivered from the RLC layer of the UTRAN or the user equipment to the MAC layer through the logical channel is transmitted to the physical layer through an appropriate transport channel.
Herein, when the data passed the dedicated logical channel is transmitted through the common transport channel as described above, it passes through the MAC-d sub layer and the Mac-c/sh sub layer and ultimately transmitted to the physical layer.
In that case, MAC PDU header information, which is added by each part of the MAC layer, can include a TCTF field, a user equipment identifier type field, a user equipment identifier field and a C/T field etc.
The TCTF field indicates the following: the type of a logical channel the data of which is transmitted through a specific transport channel; the user equipment identifier type field indicating which user equipment identifier among various types of user equipment identifiers is used; the user equipment identifier field including identification information of a user equipment designated in the user equipment identifier type field; and the CIT field which provides information for distinguishing each logical channel when data of several logical channels are transmitted to one transport channel.
A user equipment identifier, used for identifying a user equipment on the MAC-c/sh sub layer shown in FIG. 4, can be divided into two types according to a user equipment's distinguishable geographical region (i.e. a range in which each user equipment can cover) in a network.
First, a C-RNTI (Cell Radio Network Temporary Identity) is allocated by the control RNC when a user equipment is linked to a new cell. Accordingly, the C-RNTI has unique value only in a pertinent cell, and a cell region is the effective region of the C-RNTI. Therefore, when the user equipment moves to another cell, the C-RNTI has to be changed.
Second, a U-RNTI (UTRAN Radio Network Temporary Identify) is used for identifying a certain user equipment in the UTRAN, and it is composed of a S-RNTI (SRNC RNTI) and a serving RNC identifier. The S-RNTI is an identification value used for identifying a certain user equipment in the serving RNC, and each user equipment has a unique S-RNTI value in the serving RNC. In addition, the serving RNC identifier is used to identify the RNC in the UTRAN. Accordingly, in order to designate a certain user equipment in the UTRAN, serving RNC identifier information and an identification value of the user equipment in the pertinent RNC are required.
Accordingly, the U-RNTI is a unique value in the UTRAN and is not changed even in cases where the use equipment is moved to a different cell in a RNS. However, when the serving RNC identifier is changed due to the change of the serving RNC, a new U-RNTI value has to be allocated. More specifically, a U-RNTI effective range is a region managed by a serving RNC.
In a system compliant with the 3GPP standard, a user equipment is identified by using only one of the two types of user equipment identifier: with the C-RNTI, a 16 bit is required, and with the U-RNTI, a 32 bit is required. Accordingly, by using C-RNTI the limited radio channel resources can be efficiently used. In some cases, a value of the U-RNTI is used. For example, when a C-RNTI value is changed frequently, a user equipment can be identified effectively by using a U-RNTI value.
However, in the conventional system compliant with the 3GPP standard, identification information of a user equipment is added to a MAC PDU by the MAC layer of the transmitter side, and the identification information of the user equipment is identified in the receiver side of the MAC layer. Though, the transmitter side MAC layer performs multiplexing of an RLC PDU transmitted from the RLC layer and adding identification information of a user equipment to a MAC PDU (a data unit corresponding to the RLC PDU), the MAC layer is unable to recognize when and which type of user equipment identifier is used, and can not change the type of user equipment identifier dynamically.